Processing of livestock waste, for the production of biomethane for use in agricultural vehicles and biofertilizers

PROJECT DESCRIPTION

BACKGROUND

Unmanaged livestock waste is an important source of diffuse emissions of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O). According to an annual GHG report, the agricultural sector is responsible for 21% of global greenhouse gas (GHG) emissions (Food and Agriculture Organization, 2016). Intensive livestock farms are the largest emitters of these gases due to the concentration of animals in small spaces. Manure management generates around 230-106 tCO2eq/year, with pigs being responsible for 40% of these emissions. Methane and nitrous oxide are the main gases emitted in agricultural production, especiallyfrom the management of livestock and their manure. The management of this waste through anaerobic biodigestion processes prevents the generation of these emissions, while producing biogas that undergoes a subsequent purification treatment (upgrading) to become a biofuel (biomethane). The use of biomethane as fuel in vehicles, replacing conventional fossil fuels, entails the reduction of CO2e emissions (2 kg CO2 per m3 of biomethane produced). Similarly, compressed natural gas (CNG) combustion engines have a lower emission of volatile particles and NOx than diesel engines used in vehicles and agricultural machinery.

OBJECTIVES

The main objective of the LIFE SMART AgroMobility project is to demonstrate the technical, economic and environmental viability of a new management model for livestock discharges (pig manure) through biodigestion with innovative low-cost biodigesters. The resulting digestate will be valorised as a high-value biomass for use as a biofertilier/biostimulant. This will be achieved through the treatment and fixation of nitrogen (N) and phosphorus (P) by microalgae, which, in turn, act as abiological biogas-refining system and transformation of this into biomethane. The final products will be biomethane for use in agricultural vehicles and biofertilisers.

The project contributes to the implementation of the EU Renewables Energy Directive (2018/2001/EU), through the production of biomethane, the Energy Efficiency Directive (2012/27/EU), through the transformation of waste into energy, and a range of other EU policies relating to sustainable agriculture and biofuels.

RESULTS

Expected results:

Low cost biodigesters for pig manure, with a total capacity of 150 m3. A total of 2 100 m3 of slurry managed, with a generation of 36 tCH4/year, avoiding 730 tCO2/year emissions. The process allows savings of 2.57 kgCO2e per kg of meat produced (42% reduction in emissions);

Prototype of new technology (microalgae and bacteria and simultaneous removal of CO2 and H2S) to obtain biomethane. The biological refining treatment will have an area of photobioreactors for microalgae culture of 1 500 m2, which will allow the treatment of a flow of 80 m3/day of biogas. This flow corresponds to 82% of the biogas produced in the digester, the rest being consumed to generate heat;

New refining process (removal of trace contaminants such as volatile organic compounds, NH3, H2S) and biomethane compression, based on a multi-phase procedure. As a result of thelast phase of treatment, a high purity biomethane, compressed at a pressure of 250 bar, is obtained, suitable for supply to vehicles by means of the gas station developed for this purpose;

Real-scale demonstration of the use of the biomethane produced to supply fuel to two vehicle types: light vehicle and tractor. Starting from the production of biomethane obtained in the previous phases, it would allow the realisation of up to 280 000 km (light vehicle); and

Digestate (solid residue of the biodigestion process) has value as an organic fertilizer. The microalgae produced in the photobioreactor, due to its N and P content and the presence of natural phytohormones and fungicides, constitute a biofertiliser. Biofertilisers indirectly minimise the carbon footprint of the European agricultural sector by reducing the consumption of synthetic nitrogenous fertilisers.